The invention relates generally to microgrids and more particularly to a system and method for controlling microgrids.
A microgrid is defined generally as an aggregation of controllable and uncontrollable assets which may comprise electrical generators, loads, and storage devices, for example. Electrical generators in a microgrid typically include non-conventional energy sources such as micro turbines, wind turbines, photovoltaic systems, fuel cells, or hydrogen fed reciprocating engines, for example. Microgrids may supply power to shopping centers, industrial parks, college campuses or villages, for example.
In order to interconnect a microgrid to a bulk (or main) grid, a utility company will often require the microgrid to maintain the voltage and frequency at the point of interconnection (POI). Traditionally, two methods have been proposed to maintain or regulate the POI voltage and frequency. In one method, static switching capacitors are used. This approach has slow response. Another method is to use static reactive power compensators. This approach has fast response but is expensive. Moreover, these approaches regulate voltage but cannot regulate frequency.
Reactive power control is not presently available for microgrids. Commonly assigned U.S. Pat. No. 6,924,565 describes a windfarm system connected to a utility including a control system which is used to respond to P (active power) and Q (reactive power) commands of a utility and including local controls in each of the wind turbines to implement the commands sent to them. However, in this approach only one type of distributed generator is included (variable speed, equally-sized wind turbines). For microgrid applications with diverse types and sizes of generators, it becomes more important to deal with the various microgrid characteristics, to assist bulk grid operation and improve system performance at the POI, and to minimize microgrid losses.
Tielines may include one or more POIs of a microgrid and a bulk grid. It would be useful to implement an active and reactive power control strategy at tielines of microgrids fed by a wide range of generators.